The long term goal of these studies is to elucidate the molecular mechanisms by which herpes simplex virus cleaves intranuclear concatameric viral DNA and packages the DNA into preformed intranuclear capsids. We and others have found that several proteins including UL6, UL15, UL17, and UL28 proteins are essential for DNA packaging but are dispensable for assembly of capsids. We hypothesize that procapsids (bearing UL6 in the outer shell and UL28 in the inner shell) are transported by action of UL17 protein to intranuclear sites containing the ATPase- bearing terminase subunit UL15. UL15 (bound indirectly to DNA) docks with UL6 protein in the capsid and is proteolytically cleaved. The cleaved protein binds the procapsid-bound DNA- binding subunit of the terminase, UL28 protein. The two subunit terminase then cleaves DNA that is looped into the capsid, scans DNA for a second cleavage site, and exits the capsid after this second cleavage. The goals of specific aims in this proposal are to test predictions of this hypothesis. Specific aim 1 will test the significance of UL15 proteolytic cleavage to cleavage and packaging, and test relevance of UL15 docking with capsid-bound UL6 protein. The pursuit of this aim will also include characterization of the UL15 docking site. Specific aim 2 will determine how UL28 associates with the capsid and test the relevance of detected DNA binding and cleavage activities of UL28 protein to DNA cleavage/packaging. The relevance and mechanism of interaction with UL15 protein will also be tested. The goals of specific aim 3 are to determine the role and mechanism of UL17 capsid/capsid protein transport in living cells and determine the relevance of this activity to cleavage/packaging. The relevance of the activities/interactions addressed in specific aims 1-3 will include identification of mutations that disrupt the activities/interactions in vitro, followed by testing proteins bearing such mutations for the ability to rescue viral null mutants lacking the respective proteins.